Method of producing gallium or aluminum arsenides and phosphides



June 18, 1963 R. E. .JOHNSON ETAL 3,094,388

METHOD oF PRoDucINq GALLIUM 0R ALUMINUM ARSENIDES AND PHOSPHIDES Filed Deo. 11, 1959 INVENTORS Pan/Zarza L/amsazz, dll/am M Mew 2%@ Mm, Wig@ United States Patent O 3,094,388 METHOD OF PRODUCING GALLIUM R ALUMI- NUM ARSENIDES AND PHOSPHIDES Rowland E. Johnson and Edward W. Mehal, Dallas, Tex.,

assignors to Texas Instruments Incorporated, Dallas,

Tex., a corporation of Delaware Filed Dec. 11, 1959, Ser. No. 859,060 4 Claims. (Cl. 232`04) This invention relates to a new method of producing compound semiconductors and in particular to the production of gallium arsenide.

Compound semiconductors are customarily produced by a variety of methods. For instance, gallium arsenide is customarily produced by reacting liquid gallium with arsenic in the vapor stage at a tempera-ture at least as high as the melting point of gallium arsenide. However, this method has the disadvantage of requiring a relatively high temperature which increases the susceptibil-ity toward contamination. In addition, this method i-s not readily adaptable as la continuous production process.

In `an effort to overcome the above-mentioned disadvantages, it has been suggested that gallium arsenide be prepared by reducing gallium oxide with a gaseous stream of heated hydrogen and arsenic vapors. Another suggested technique has been to volatilize gallium and arsenic `and thereafter codeposit on a relatively cooled surface to form the gallium arsenide.

Each of the above-mentioned techniques, as well as other techniques known to the art, are subject to their own difficulties. The hydrogen reduction of gallium oxide is dii'licult to complete, and the resulting compound semiconductor is heavily contaminated with oxygen. Similarly codeposition of gallium and arsenic is unusually difficult to control because of the difference in volatility of the two ingredients.

'The object of the instant invention is to provide an improved process for production of compound semiconductors and especially gallium arsenide.

Other objects and advantages of the instant invention will be apparent from the description which f llows when taken with the drawings in which:

FIGURES 1 to 3 schematically illustrate the best modes for performing the method tof the invention.

Briefly stated, the instant invention involves the process of simultaneous reduction of a halide of a group III element and a halide of a groupy V element. In a preferred embodiment, the invention involves producing the compound semi-conductor by the vapor phase reduction of karsenic halide by hydrogen in the presence of gallium halide or metallic gallium under conditions whereby the gallium arsenide is stoichiometrically produced.

According to one mode of the instant invention, a mixture of arsenic trichloride and gallium trichloride is introduced into a stream of hydrogen in excess of that required for complete reduction `of the chlorides. 'Ihe gaseous mixture is then passed through -a hot reaction zone, at for example about 1,000 C. It is theorized that in the hot reaction zone the hydrogen reduces the arsenic trichloride to free arsenic. The combination of high temperatures and low partial pressure keep the arsenic in the vapor phase. It is thought that the gallium trichloride reacts with the hydrogen to form gallium dichloride. An important feature of this invention is that free gallium is not formed in the hot reaction zone. Any free gallium produced immediately reacts with the various chlorides present 'to form a chloride of gallium which is reduced to the more stable gallium dichloride. There is no gallium arsenide deposited because under these conditions, any gallium arsenide produced would be unstable.

Thereafter, the gases are passed into contact with a relatively cool surface maintained at la .temperature of from about 200 to 900 C. The gallium dichloride disproportionates and the gallium combines with the free arsenic to form gallium arsenide which deposits in solid form. It is important to note that the deposition temperature is still high enough to maintain the other components of the gas stream in Vapor phase, namely, hydrogen and hydrogen chloride which are gaseous even at room temperature, and unreacted gallium and arsenic chlorides as well. Thus, pure gallium arsenide is deposited. Desirably, the temperature of the crystals is maintained high enough to also keep any excess arsenic from depositing on the crystal product.

An extremely close control of product purity is possible when the compound semiconductor is produced in accordance with the process of the present invention. Due allowance for the relative volatility of the gallium and the arsenic in vapor phase at the relatively cool condensation 4point can be made by employing arsenic in slight excess so that a slight amount of arsenic `can remain in the vapors lat the condensation temperature and not thereby upset the stoichiometric ratio required for gallium arsenide. Similarly, a measure of control is afforded by variation in the reaction temperature and the condensation temperature or by operating at a higher or lower hydrogen gas pressure and even the ratio of hydrogen to reactants. y

Although the above-described process embodies important advantages, it has been found that the utilization of gallium trichloride as van initial constituent presents problems in thatrgallium trichloride readily hydrolyzes with moisture and is very corrosive. In a second embodiment of the invention, such problems are minimized by forming the galliumtrichloride in the reaction chamber. According to this second mode, the gaseous stream which contains only the hydrogen and `arsenic trichloride is passed into Contact with liquid gallium heated to 900- 11t00 C. At this reaction temperature, the arsenic trichloride is reduced by the hydrogen to elemental arsenic vapors yand HCl. The HC1 produced when the AsCl3 is reduced reacts with the liquid gallium to produce gallium trichloride. This reaction continues until all of' the galtliumlium is converted to gallium trichloride. Gallium arsenide is then produced by the same mechanism described in the rst embodiment of the invention.

Although the foregoing description has been largely given in terms of the production of gallium arsenide, it should be noted that other compound semiconductors can be similarly produced by employment of other combinations of reactants such as aluminum bromide and phosphorous to produce aluminum phosphide, etc.

For la further understanding of the invention, the following `speciic examples are presented.

Example I Apparatus as shown in FIGURE 1 is used. The apparatus consists of a quartz tube 10 (25 mm. OD.; 22 mm. LD.) having an inlet 11 connected to a suitable hydrogen supply and lan exhaust Outlet 12. Heaters 14 and 15 are provided to maintain the temperatures noted in the legend. A flask 18 terminating in a dripper 20 is positioned in a branch tube 22 adjacent one end of tube 10. In conducting the process of the invention, hydrogen is admitted through inlet "11 at about 100 cc./ min. (0.0045 mole/min.). The flask 18 contains a mixture of GaCl3 and AsCl3 in the weight ratio of 37.5 to

ace/teas 3 50. The dripper 20 is controlled to give `a drip rate of about 0.2 ze/min. corresponding to about 0.44 g./min. (average specific gravity 2.2) and about 0.00244 mole/ min., `assuming an average molecular weight of 180. This gives a mole ratio in the reaction zone of where x equals GaCl3 and AsC13. Galliutn arsenide is deposited in the region of tube within heater 15.

.Example ,II

Example III Apparatus las shown in FIGUR-E 3 is used. A tube 40 like tubes 10 and A30 is employed. A flask 42 is attached at one end of tube 40 and contains AsC13. A boat 44 of liquid gallium is located in tube 40. Hydro gen is bubbled through the AsCl3 and Yalsoadmitted to the vvend of tube 40. Hydrogen llow is about l liter/min. The mole ratio of H2 to AsCl3 is about 76 to l. Gallium arsenide is deposited at the right end of tube 40.

Although .the present `invention has been shown and phase mixture of hydrogen, halide of aluminum and phosphorus into a high temperature zone maintained at a temperature in the range of from about 900 C. to about 1l00 C. to cause the hydrogen to react with the halide producing a reactant stream vcomprising the halide of aluminum as a lower order halide and phosphorus in the elemental state, passing the reactant stream produced into contact with a relatively cool surface maintained at a temperature of from `about 200 C. to 900 C. to ensure that the lower order halide of aluminum disproportionates releasing part of the 'aluminum in the elemental state and forming the higher order halide of the remaining part of the aluminum whereby the elemental aluminum combines with the elemental phosphorus and condenses on the cool surf-ace as the compound semiconductor aluminum phosphide.

3. A method of producing the compound semiconductor gallium phosphide which comprises passing a vapor phase mixture of hydrogen, halide of gallium-and phosphorus in a high temperature Zone maintained at a ternperature in the range of .from about 900 .C.to about 1l00 C. to cause the hydrogen to react with the halide producing a .reactant stream comprising the halide of gallium as -a lower order halide `and phosphorus in the elemental state, passing the reactant stream produced into contact with a relatively cool surface maintained at a temperature of from about 200 C. to 900 C. to ensure described lin terms of the best mode contemplated for 'i carrying out -the invention, nevertheless, it will be apf Preci-ated that changes and modiications can be made which `do not depart from the inventive concepts taught herein. Such changes and modications are deemed to be within the purview of the invention. What is claimed is:

l. A method of producing the compound semiconductor gallium arsenide which comprises passing `a vapor phase mixture of hydrogen and halides of gallium and t arsenic .into a high temperature Zone maintained at a temperature in the range of from about 900 C. -to about 1100 C. to cause the hydrogen to react with the halides producing a reactant stream comprising vthe halide of galliumV as a lower 'order halide and arsenic in the elemental state, passing the reactant stream produced into contact with a relatively `cool surface maintained at a y temperature of from about 200 C. 'to about 900 C.

that the lower `order halide of gallium disproportionates releasing 4part of the gallium in the elemental state and forming the higher order halide of the remaining part of the gallium whereby the elemental gallium combines with the elemental phosphorus and condense/s on the cool surf-ace 'as the compound semiconductor gallium phosphide.

4. A method of producing the compound semiconductor aluminum arsenide which comprises passing a vapor phase mixture of hydrogen and halides of aluminum and arsenic into a high temperature zone maintained at a temperature in the range of from about 900 C. to about 1l00 to vcause the hydrogen to react with the halide producing a reactant stream comprising the halide of aluminum as a lower order halide and arsenic in the elemental state, passing the reactant stream `produced into contact with a relatively cool surface rmaintained at a temperature of from about 200 C. to 900 C. to ensure that the lower order halide of aluminum disproportionates releasing part of the aluminum in the elemental state and formi-ng the higher order halide of the remaining part of the aluminum whereby the elemental aluminum combines with the elemental arsenic and condenses on the cool surface as the compound semiconductor `aluminum arsenide.

References Cited in the file of this patent UNITED STATES PATENTS 2,313,410 Walther Mar. 9, 1943 2,798,989 Welker July 9, 1957 2,938,816 Gunther May 31, 1960 

1. A METHOD OF PRODUCING THE COMPOUND SEMICONDUCTOR GALLIUM ARSENIDE WHICH COMPRISES PASSING A VAPOR PHASE MIXTURE OF HYDROGEN AND HALIDES OF GALLIUM AND ARSENIC INTO A HIGH TEMPERATURE ZONE MAINTAINED AT A TEMPERATURE IN THE RANGE OF FROM ABOUT 900*C. TO ABOUT 1100*C. TO CAUSE THE HYDROGEN TO REACT WITH THE HALIDES PRODUCING A REACTANT STREAM COMPRISING THE HALIDE OF GALLIUM AS A LOWER ORDER HALIDE AND ARSENIC IN THE ELEMENTAL STATE, PASSING THE REACTANT STREAM PRODUCED INTO CONTACT WITH A RELATIVELY COOL SURFACE MAINTAINED AT A TEMPERATURE OF FROM ABOUT 200*C. TO ABOUT 900*C. TO ENSURE THAT THE LOWER ORDER HALIDE OF GALLIUM DISPROPORTIONATES RELEASING PART OF THE GALLIUM IN THE ELEMENTAL STATE AND FORMING THE HIGHER ORDER HALIDE OF THE REMAINING PART OF THE GALLIUM WHEREBY THE ELEMENTAL GALLIUM COMBINED WITH THE ELEMENTAL ARSENIC AND CONDENSES ON THE COOL SURFACE AS THE COMPOUND SEMICONDUCTOR GALLIUM ARSENIDE. 